In a conventional obstacle detection device (hereinafter referred to as a “first obstacle detection device”) a radar that detects an obstacle within a predetermined angular range is used to detect an obstacle behind a vehicle as well as another vehicle on an adjoining traffic lane. If the first obstacle detection device detects an obstacle, it lights an indicator lamp to indicate a direction in which the obstacle has been detected, and displays, in numerals, a distance to the obstacle.
Another obstacle detection device (hereinafter referred to as a “second obstacle detection device”) uses a radar to detect an obstacle in the vicinity of the vehicle and displays an image representing the shape of the detected obstacle. The second obstacle detection device stores, as point data, the location of the obstacle as accurately detected by using a laser radar, and draws, based on the stored point data, a line diagram representing the external shape of the obstacle to create a map of the surrounding area of the vehicle.
With the first obstacle detection device, however, it is difficult for a driver to obtain an intuitive grasp of a positional relationship between his or her vehicle and an obstacle, because the location of the obstacle is represented by lighting of a lamp indicating the direction and a numerical value indicating the distance.
Meanwhile, with the second obstacle detection device, which displays a map in which the external shape of a detected obstacle is drawn with a line diagram, a driver can easily grasp a positional relationship between his or her vehicle and the obstacle. However, in order to detect locations of obstacles as points, the second obstacle detection device is equipped with a laser radar whose beam divergence angle is very narrow. As a result, since laser radars are generally costly, the cost of the whole device becomes very high.
Here, the use of a comparatively low-priced, ultrasonic radar or radio-wave radar is conceivable. However, to make the divergence angle of ultrasonic or radio-wave beams narrow, it is necessary to greatly enlarge a horn for emitting ultrasonic waves or an antenna for emitting the radio waves, which causes a problem of a large installation space having to be secured in the vehicle. In other words, regardless of whether the type of beam is laser, sonic, or radio, a problem of cost or installation occurs. Thus, it is not practical to use a radar that emits beams whose divergence angle is very narrow in an obstacle detection device.
Therefore, an object of the present invention is to provide an obstacle detection device that displays a positional relationship between a vehicle and an obstacle such that the driver can easily obtain an intuitive grasp of the positional relationship, even in the case where a radar whose beam divergence angle is comparatively wide is used to detect the obstacle.